<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .main {
            width: 600px;
            display: flex;
            flex-wrap: wrap;
            flex-direction: column;
            margin: auto;
        }

        .top {
            width: 100%;
            height: 50px;
            background-color: pink;
        }

        .content {
            display: flex;
            width: 100%;
            /* flex: 1; */
        }

        .left {
            flex: 1;
            /* width: 20%; */
            height: 500px;
            background-color: aquamarine;
        }

        .right {
            flex: 4;
            /* width: 80%; */
            height: 500px;
            background-color: skyblue;
        }

        .footer {
            width: 100%;
            height: 50px;
            background-color: lavender;
        }
    </style>
</head>

<body>

    <div class="main">
        <div class="top"></div>
        <div class="content">
            <div class="left"></div>
            <div class="right"></div>
        </div>
        <div class="footer"></div>
    </div>
</body>

</html>